Piezoelectric vibrators have been widely used as oscillators or bandpass filters. For example, Japanese Unexamined Patent Application Publication No. 2013-62712 (hereinafter “Patent Document 1”) discloses, as a form of an existing piezoelectric vibrator, a surface mount quartz vibrator having a structure in which a quartz vibrator is sealed from the outside air. The surface mount quartz vibrator disclosed in Patent Document 1 includes a ceramic substrate on which a quartz vibrator is mounted, an insulating film disposed round on the surface of the ceramic substrate so as to surround the quartz vibrator, a sealant formed from a resin or other material and superposed on the insulating film, and a metal lid joined to the ceramic substrate with the insulating film and the sealant interposed therebetween. The metal lid is bonded to the ceramic substrate with pressure while the sealant is heated to melt. The quartz vibrator can thus be sealed in the metal lid disclosed in Patent Document 1.
However, bonding the metal lid to the ceramic substrate with pressure while heating the sealant to melt may cause a gap between the sealant and the metal lid while the sealant is heated. If this gap expands, the sealant and the metal lid may be bonded with small bonding strength and the metal lid may be detached from the ceramic substrate.